Paper structures, such as toilet tissue, paper towels, and facial tissue, are widely used throughout the home and industry. Many attempts have been made to make such tissue products more consumer preferred.
One approach to providing consumer preferred tissue products having bulk and flexibility is illustrated in U.S. Pat. No. 3,994,771 issued Nov. 30, 1976 to Morgan et al, which patent is incorporated herein by reference. Improved bulk and flexibility may also be provided through bilaterally staggered compressed and uncompressed zones, as shown in U.S. Pat. No. 4,191,609 issued Mar. 4, 1980 to Trokhan, which patent is incorporated herein by reference.
Another approach to making tissue products more consumer preferred is to dry the paper structure to impart greater bulk, tensile strength, and burst strength to the tissue products. Examples of paper structures made in this manner are illustrated in U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan, which patent is incorporated herein by reference. U.S. Pat. No. 4,637,859 shows discrete dome shaped protuberances dispersed throughout a continuous network, and is incorporated herein by reference. The continuous network can provide strength, while the relatively thicker domes can provide softness and absorbency.
One disadvantage of the papermaking method disclosed in U.S. Pat. No. 4,637,859 is that drying such a web can be relatively energy intensive and expensive, and typically involves the use of through air drying equipment. In addition, the papermaking method disclosed in U.S. Pat. No. 4,637,859 can be limited with respect to the speed at which the web can be finally dried on the Yankee dryer drum. This limitation is thought to be due, at least in part, to the pattern imparted to the web prior to transfer of the web to the Yankee drum. In particular, the discrete domes described in U.S. Pat. No. 4,637,859 may not be dried as efficiently on the Yankee surface as is the continuous network described in U.S. Pat. No. 4,637,859. Accordingly, for a given consistency level and basis weight, the speed at which the Yankee drum can be operated is limited.
The following publications show additional methods for making a paper web and are incorporated herein by reference: WO 95/17548 published Jun. 29, 1995 in the name of Ampulski et al. and having a Dec. 20, 1993 US priority date; WO 96/00812 published Jan. 11, 1996 in the name of Trokhan et al. and having a Jun. 29, 1994 U.S. priority date; WO 96/00814 published Jan. 11, 1996 in the name of Phan and having a Jun. 29, 1994 priority date; U.S. Pat. No. 5,556,509 issued Sep. 17, 1996 to Trokhan et al.; and U.S. Pat. No. 5,549,790 issued Aug. 27, 1996 to Phan.
U.S. Pat. Nos. 4,326,000; 4,000,237; and 3,903,342 describe sheet materials having elastomeric bonding materials connecting surfaces of the sheet together in a pattern. Such a method has the disadvantage that application of the bonding materials can be relatively expensive and difficult to control at production speeds. Additionally, the elastomeric bonding material may reduce the absorbency of the web.
Conventional tissue paper made by pressing a web with one or more press felts in a press nip can be made at relatively high speeds. The conventionally pressed paper, once dried, can then be embossed to pattern the web, and to increase the macro-caliper of the web. For example, embossed patterns formed in tissue paper products after the tissue paper products have been dried are common.
However, embossing processes typically impart a particular aesthetic appearance to the paper structure at the expense of other properties of the structure. In particular, embossing a dried paper web disrupts bonds between fibers in the cellulosic structure. This disruption occurs because the bonds are formed and set upon drying of the embryonic fibrous slurry. After drying the paper structure, moving fibers normal to the plane of the paper structure by embossing breaks fiber to fiber bonds. Breaking bonds results in reduced tensile strength of the dried paper web. In addition, embossing is typically done after creping of the dried paper web from the drying drum. Embossing after creping can disrupt the creping pattern imparted to the web. For instance, embossing can eliminate the creping pattern in some portions of the web by compacting or stretching the creping pattern. Such a result is undesirable because the creping pattern improves the softness and flexibility of the dried web.
Scientists and engineers in the papermaking arts continue to search for improved methods of making soft, strong, and absorbent tissue paper which can be dried efficiently at reduced expense.
Accordingly, one object of the present invention is to provide a paper web and method for making a multi-region paper web which allow relatively faster drying with relatively lower energy and expense.
Another object of the present invention is to provide a method for making a multi-region paper which can be formed on an existing paper machine (conventional or through air drying capability) without the need for substantial modification of the papermaking machine.
Another object of the present invention is to provide a paper web and method for making a paper web where the web has at least two different, nonembossed regions distinguishable by one or more of the following properties: thickness, elevation, density, and basis weight.
Another object is to provide a paper web and method of making the paper web where the web has an enhanced bulk caliper, bulk density, and absorbent capacity with a relatively patterned face and relatively smooth opposite face, thereby providing both the properties of bulk and softness desired by consumers of paper products.
Another object of the present invention is to provide a paper web and method of making the paper web where the web is substantially free of binding materials, such as elastomeric binding materials, which adversely affect the absorbency.